Hemodialysis is a medical technique that filters wastes and water from our blood in the same way as our kidneys did when they were functioning normally. Hemodialysis aids with blood pressure control and the balance of vital minerals like potassium, sodium, and calcium in the blood. In this article, we will get to know about hemodialysis procedure, hemodialysis machine, and other factors.


Hemodialysis Procedure

To purify the blood, a hemodialysis machine uses a dialyzer (sometimes known as an artificial kidney). A surgeon will make an access, or entry, into the blood vessels to get the blood to the dialyzer. This is achieved with minimal surgery, which is usually performed on the arm. The two most common types of access are a fistula and a graft:

The fistula| Hemodialysis Procedure

  • It is the most common type of access.
  • It is formed by linking an artery to a neighboring vein under the skin to form a larger blood vessel.
  • This access is recommended since it is less problematic and lasts longer. In other words, A fistula is a hole in the body. 
  • At least six months before dialysis, one should consult a vascular surgeon.
  • A fistula must be implanted as soon as possible so that it has enough time to mend and be available for therapy when needed.

A Graft | Hemodialysis Procedure

  • It is performed if the blood vessels are not suited for a fistula. A short, soft tube composed of synthetic material is put beneath the skin to connect an artery and a neighboring vein.
  • The fistula or graft can be utilized for dialysis when it has healed for at least several months.
  • Every time you come in for treatment, two needles will be inserted. Plastic tubes are used to connect to the needles. 
  • The blood is drawn into the dia lyzer, which cleans it before returning it to the body via the other tube.
hemodialysis  causes

A catheter| Hemodialysis Procedure

  • It is a soft tube put into a major vein in the neck or chest as a third method of access.
  • When dialysis is required for a short length of time, this form of access is typically employed.
  • When a fistula or graft cannot be implanted, catheters can be utilized as permanent access.
  • Needles are not necessary since catheters may be linked directly to the dialysis tubes. Catheters are more hazardous to one’s health than other forms of access.

Hemodialysis Machine

  • Two tubes are connected to the hemodialysis access. Blood can flow from the body into the machine through one of the tubes.
  • If the nephrologist has prescribed a blood thinner as part of the therapy, it will be given to prevent the blood from clotting while it is in the machine.
  • To maintain the optimum flow rate, a pressure sensor and a pump operate together.
  • The blood is filtered as it enters the dialyzer.
  • The dialyzer receives the dialysate solution. It removes waste from the blood.
  • The machine’s used dialysate solution is pushed out and disposed of.
  • To ensure that the blood is safe to return to the body, it passes through another pressure monitor and an air trap.
  • The second tube connected to the access site returns the cleansed blood to the body.

Dialysate| Hemodialysis Machine

Dialysate is a mixture of water, electrolytes, and salts. During dialysis, dialysate cleans the blood within the dialyzer by removing waste materials and balancing electrolytes.A nephrologist will recommend the dialysate that best suits one’s needs.

Dialyzer| Hemodialysis Machine

  • A dialyzer (also known as an artificial kidney) is where the blood and dialysis solution circuits meet and molecules from the dialysis solution and blood pass through a semipermeable membrane.
  • There are two sides to the dialyzer, or filter: one for the blood and the other for a fluid called dialysate.
  • These two sides are separated by a narrow membrane. Because blood cells, protein, and other vital substances are too large to travel through the barrier, they remain in the blood.
  • Smaller waste items like urea and creatinine, as well as excess fluid, pass through the membrane and are eliminated.
hemodialysis machine

Dialysis Tubing| Hemodialysis Machine

  • Visking tubing, which is another name for Dialysis tubing, is a semi-permeable artificial membrane tubing that allows microscopic molecules in solution to move by differential diffusion during separation procedures .
  • Dialysis tubing is commonly used in the clean-up and processing of proteins and DNA samples, as well as complicated biological samples such as blood or serums.
  • Dialysis tubing is often used to demonstrate the principles of diffusion, osmosis, Brownian motion, and the flow of molecules across a limited membrane.

Type of Hemodialysis Needles | Hemodialysis Machine

The first type of needle used for initial cannulation is a sharp metal needle when beginning the rope ladder/rotating site technique or same-site cannulation to construct tunnel tracks for the buttonhole technique (Dialysis needles are inserted into the same holes on the fistula every time it is used for dialysis).

  • Alternatively, to form the buttonhole tunnel track, plastic cannulas or pegs are kept in the vessel for a while.
  • Metal needles are either sharp or blunt and are constructed of stainless steel. 
  • Sharp needles have a sharp cutting edge and are utilized in the rope ladder method, whereas blunt needles have a rounded top and no sharp edge and are used in the buttonhole method. 
  • Metal needles are coated with silicone for easy insertion and reduced flow resistance. 
  • Sharp needles are indicated for some buttonhole patients because dull needles may bounce off the vasculature upon entry into the track.

The illustration below depicts the difference between the sharp and blunt needle tips.


  • For the first several cannulations in a new fistula, angio-catheters are advised.
  • Angiocatheters can be utilized to cannulate frail AVFs with convoluted segments or variable depths from the skin surface, despite their usual use for IV catheterization.
  • Because the tubing is flexible and dull, there is less risk of infiltration from dialysis arm movement.


  • A fistula cannula, fistula catheter, or plastic needle is designed particularly for hemodialysis cannulation. In its most basic form, a sharp metal needle is wrapped inside a flexible plastic sheath.
  • The metal needle is used to gain access to an AVF(arteriovenous fistula) as well as to guide the plastic sheath into the vessel.
  • The metal needle is withdrawn when the sheath is placed into the vessel, leaving just the flexible blunt sheath within.

Figure: Fistula cannula needle

Figure: When the plastic cannula is not used, just the tip of the metal needle is exposed for insertion.


  • For at least the first several cannulations of a new fistula, small gauge needles (17G) should be used.
  • Following that, as the fistula grows and previous cannulations go easily, the gauge can be gradually raised.
  • Since smaller gauge needles restrict flow more, a slower blood flow rate of 200-250 ml/min is needed.


  • There are many needle lengths available: 3/4″ and 3/5″ for fistulas less than 0.4 cm below the skin surface, 1″ for fistulas 0.4-1 cm below the skin surface, and 1 1/4″ for fistulas greater than 1 cm below the skin surface. 
  • The smallest needle length should be utilized to avoid needle penetration into the vessel’s back wall. However, a 1 1/4″ needle may be required to access deep AVFs, such as those seen in the upper arm of an obese patient. 
  • Metal AVF needles are typically 1″ in length, although shorter 3/5″ AVF needles may be preferable for entirely progressing into a shallow new fistula.  Plastic cannula needles come in lengths up to 38 mm (about 1 1/2″).

In dialysis, what kind of catheters are used?

  • Dialysis catheters are transcutaneous artificial implanted medical tubes that are used to reach the intravascular or intraperitoneal space for renal replacement treatment (RRT).
  • Dialysis catheters are divided into two categories: 
  • Catheters which are used extracorporeal RRT (such as hemodialysis, hemofiltration, hemodiafiltration, or ultrafiltration) and 
  • Those used in peritoneal dialysis. 
  • Extracorporeal RRT catheters are primarily wide-bore central venous lines that allow blood to be taken from and returned to the patient efficiently. 
  • It further allows the patient’s blood to be briefly eliminated from the body and processed in an extracorporeal RRT machine, which can perform hemodialysis, hemofiltration, hemodiafiltration, or ultrafiltration depending on the patient’s needs.
  • Depending on the duration of therapy, the catheter can be directly integrated into the target vein via the skin or through a brief subcutaneous tunnel before reaching the vein, with an inbuilt felt cuff linking it to the local tissue.
  • Catheters for peritoneal dialysis dialysate is injected into the intraperitoneal space and remains in contact with the peritoneal membrane for a short time before being removed. This method of therapy involves doing dialysis directly across the peritoneal membrane.

Blood Flow Rate in Hemodialysis| Hemodialysis Procedure

  • A blood pump is used during hemodialysis to move the blood through the dialyzer and back to the body at a steady speed. 
  • The blood flow rate is set by the nephrologist. It normally ranges from 300 to 500 mL/min (milliliters per minute). 
  • Inquire with the technician about how to view the blood flow rate on the machine. 
  • Blood flow rates of more than 400 mL/min can boost the elimination of toxins in various dialyzers. The size of the access, the tubing, and the needles all limit the blood flow rate.

Sodium Profiling in Hemodialysis | Hemodialysis Procedure

  • Instead of being constant during a hemodialysis session, the sodium content in the dialysis fluid follows a time-dependent curve. 
  • The major goal of this procedure is to minimize osmotic disequilibrium by maintaining plasma osmolality within normal limits. 
  • Muscle cramps are less likely, salt elimination is enhanced, and vascular stability is increased, among other benefits of sodium profiling. Various investigators have employed many distinct profiles. 
  • If sodium profiling is not done properly, salt buildup might occur, leading to enhanced thirst, interdialytic weight gain (the result of salt and water intake between two hemodialysis sessions), and hypertension. 
  • Sodium buildup might explain why certain short-term sodium profiling investigations found lower intradialytic morbidity.

Ultrafiltration in Hemodialysis| Hemodialysis Procedure

  • One of the functions of the kidneys that dialysis therapy substitutes is ultrafiltration, which is the evacuation of fluid from a patient. 
  • Ultrafiltration occurs when a driving pressure causes fluid to flow through a semipermeable membrane (a barrier that permits certain substances to pass through but not others).
  • Fluid is extracted from the body by ultrafiltration through the dialysis membrane in hemodialysis.
  • The dialysate side has a lower pressure, therefore water travels from the blood (which has a greater pressure) to the dialysate (place of lower pressure).
  • This is how fluid is removed during hemodialysis.
hemodialysis ultrafiltation
  • The amount of fluid evacuated is controlled by the ultrafiltration rate and the length of dialysis treatment time. 
  • Each treatment’s ultrafiltration rate will be determined by the amount of fluid you’ve gained since the last treatment.
  • The aim is to reach the desired weight, sometimes known as dry weight.
  • Patients may feel low blood pressure and cramps if they consume too much fluid between dialysis treatments and the body cannot handle a greater ultrafiltration rate because the fluid is being cleared too quickly.
  • If the extra fluid cannot be safely evacuated at one time, patients may need a lengthier dialysis treatment and/or an extra treatment day.

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